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Buildings  of  Reinforced 


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By  Prof.  Charles  Derleth,  Jr.  (  1  ) 

Introduction. 

In  the  Fall  of  1908  a  conference,  which  I  attended,  was  held  one 
evening  at  the  Faculty  Club  of  the  University  of  California.  Two 
groups  of  gentlemen  were  present:  1,  representatives  of  the  fire 
surance  interests  of  the  Pacific  Coast;  2,  members  of  the  technical 
and  economic  departments  of  the  University  of  California. 

It  was  the  purpose  of  the  conference  to  discuss  in  general  the  busi¬ 
ness  problems  of  fire  insurance  and  to  point  out  if  possible  to  what 
extent  an  educational  institution,  particularly  a  technical  school,  might 
aid  in  increasing  the  equipment  and  improving  the  efficiency  of  young 
men, — applicants  for  admission  to  the  fire  insurance  profession.  It 
would  be  out  of  place  for  me  to  give  the  argument  which  ensued.  That 
is  not  the  object  of  my  paper.  Indeed,  it  would  he  impossible  in  a 
sufficiently  short  statement  to  do  justice  to  the  arguments  presented. 
The  views  expressed  by  the  fire  insurance  men  brought  home  to  me, 
however,  a  situation  with  which  I  had  not  been  clearly  acquainted. 
You  will  pardon,  therefore,  an  introduction  defining  this  situation  as 
I  was  led  to  understand  it,  because  the  principle  involved  bears  upon 
the  subject  of  building  construction  as  much  as  it  concerns  the  busi¬ 
ness  of  fire  underwriting,  and  thus  affords  to  me  a  pretext  for  present¬ 
ing  to  you  at  this  gathering  a  paper  on  engineering  construction. 

The  Statement. 

It  was  argued  that  there  is  a  sharp  distinction  to  be  made  between 
the  work  of  a  fire  insurance  solicitor,  on  the  one  hand,  and  of  the  fire 
insurance  actuary,  or  fire  insurance  engineer,  on  the  other.  It  may  be 
that  I  am  misstating  the  views  expressed,  but  I  gathered  that  in  the 
main  the  gentlemen  who  are  concerned  with  getting  fire  insurance 
business,  the  men  who  daily  are  dealing  with  the  commercial  side  of 
that  business,  are  men  not  by  taste  or  training  concerned  with  mathe¬ 
matical,  economical  and  engineering  principles,  though  these  prin- 


4 


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1  Professor  of  Civil  Engineering,  University  of  California. 


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2 


BUILDINGS  OF  REINFORCED  CONCRETE 


ciples  affect  and  influence  the  intelligent  design  of  fire  resistant,  fire  protect¬ 
ive,  and  fire  preventive  building  construction.  I  learned  that  technical 
studies  do  not  help  the  insurance  apprentice  whose  daily  routine  is  flavored 
with  statistical  and  bookkeeping  accounts. 

Reply  to  the  Statement. 

If  this  be  true,  it  is  hardly  to  be  expected  that  a  technical  paper  outlining 
structural  requirements  for  a  special  type  of  building  will  prove  of  absorbing 
interest  to  members  of  an  association  interested  primarily  in  the  business 
success  of  fire  insurance.  I  have  perused  the  reports  of  your  annual  meet¬ 
ings  for  the  four  years  past,  1906  to  1909,  inclusive,  and  note  that  the  papers 
read  are  almost  wholly  on  such  subjects  as  “Inspections,”  “Rating 
Schedules,”  “Adjustments,”  “Conflagration  Hazard  and  Co-Insurance,” 
“Underwriting  Conditions,”  “Special  Agents,”  “Spontaneous  Combus¬ 
tion,”  “On  the  Writing  of  Papers,”  “The  Doctrine  of  Waivers  as  Relates  to 
the  Adjustments  of  Fire  Insurance  Claims,”  etc.  It  will  be  noted  that, 
vital  as  these  subjects  are  to  the  proper  writing  of  insurance,  there  is  little 
of  a  strictly  engineering  nature  in  these  papers.  At  the  four  meetings  cited 
you  have  had  read  only  two  papers  which  dealt  particularly  with  construc¬ 
tion;  one  by  my  colleague,  Professor  Charles  Gilman  Hyde,  on  the  “Water 
Supply  of  Cities;”  the  other  by  my  friend,  Mr.  W.  J.  Miller,  an  architect 
and  structural  engineer  of  San  Francisco,  on  the  subject  of  “Class  A  Con¬ 
struction.”  Both  of  these  papers  were  read  at  the  January  meeting  in  1907. 
I  have  an  idea  that  the  subjects  were  prompted  by  our  great  conflagration  of 
the  preceding  year.  At  any  rate  in  the  early  part  of  1907  the  subject  of  high 
grade  municipal  construction  was  of  apparent  interest  to  everyone,  and 
people  in  general  were  eager  to  listen  to  discourses  on  the  requirements  and 
specifications  for  sane  structural  design.  Unhappily  the  taste  for  such  dis¬ 
courses  appears  to  be  satiated. 

Of  course,  by  these  remarks  it  is  not  my  intention  to  criticise  the 
absence  or  to  deplore  the  omission  of  engineering  discussions  from  the 
deliberations  of  your  annual  meetings.  It  is  obvious  that  the  first 
duty  of  an  association  of  fire  insurance  companies  of  the  Pacific  Coast, 
or  of  any  similar  body  elsewhere,  must  be  to  instruct  and  encourage 
its  members  to  get  business  and  to  write  papers  that  strengthen  the 
company  at  the  same  time  that  they  give  the  individual  a  safe  insur¬ 
ance.  Your  main  object,  I  take  it,  is  to  make  the  insurance  business 
grow  and  to  set  sound  rates.  However,  notwithstanding  all  these  facts, 
it  seems  to  me,  as  a  layman  in  insurance,  but  as  a  student  of  en¬ 
gineering,  that  you  must  acquaint  yourselves  more  and  more  with  the 
requirements  of  construction.  It  is  true  that  in  the  larger  sense  your 
companies  must  be  guided  by  the  opinions  of  advising  engineers,  not 


BUILDINGS  OF  REINFORCED  CONCRETE 


3 


by  one,  but  by  different  persons  representing  different  branches  of 
engineering.  You  must  have  your  general  advisers  on  mechanical  engineer¬ 
ing,  electric  work,  structural  design.  Nevertheless,  much  will  be  gained,  I 
think,  the  more  the  insurance  men  themselves  learn  to  appreciate  those 
elements  necessary  for  the  creation  of  the  best  construction  of  different  types. 
You  should  have  a  clear  picture  before  you  of  different  grades  of  building. 
It  is  futile  to  recommend  that  all  buildings  be  of  the  best  types.  The  owner 
of  a  lot,  after  all,  must  erect  a  building  for  a  cost  within  his  financial  means 
and  of  such  size  that  he  will  get  a  reasonable  return  on  his  investment. 

Discussion  of  the  Statement. 

I  should  be  glad  if  these  remarks  produce  a  discussion.  I  should  like  to 
know  from  insurance  men  more  definitely  to  what  extent  a  general  acquaint¬ 
ance  with  engineering  would  be  of  assistance  to  them  in  their  work.  It  may 
be  that  my  opinions  are  imperfect  and  that  it  would  be  a  detriment  to  the 
average  insurance  man  to  divert  a  part  of  his  energies  to  semi-technical 
questions.  I  am  perfectly  aware  that  this  is  an  age  of  specialization,  but  he 
is  a  poor  specialist  who  cannot  appreciate  the  needs  of  those  professions  which 
are  closely  allied  to  his  own  work. 

You  will  pardon  my  long  introduction.  I  offer  it  partly,  as  I  have  said,  in 
an  attempt  to  solicit  discussion ;  but  mainly  to  justify  my  presentation  of  a 
general  descriptive  picture  portraying  the  present  stage  of  development  of 
reinforced  concrete  design  for  city  buildings.  In  what  follows  I  shall  give 
you  an  elementary  account,  shorn  wherever  possible  of  mathematical  and 
mechanical  terms.  I  offer  nothing  new  or  original;  my  facts  are  taken, 
often  without  special  acknowledgment,  from  standard  text  books,  essays  and 
specifications.  For  more  elaborate  accounts  the  reader  is  referred  to  the  foot 
notes  and  to  the  bibliography  appended  to  my  article. 

Classification  of  Building  Types. 

Different  city  ordinances  have  attempted  to  classify  buildings  ac¬ 

cording  to  grades  of  construction.  No  uniform  system  has  been 
adopted  in  this  country.  In  the  San  Francisco  ordinance  the  scheme 
used  is  to  be  deplored,  since  to  the  mind  of  the  layman  it  seems  to 
indicate  degrees  of  superiority.  For  instance,  men  speak  of  class  A 
and  class  B  buildings  with  the  general  notion  that  whatever  is  class 
B  is  distinctly  inferor  to  class  A.  The  San  Francisco  ordinance 

places  frame  dwellings  the  lowest  in  the  list,  yet  I  can  conceive  of  a 

well-built  wooden  building,  properly  located  with  respect  to  prescribed 


4 


BUILDINGS  OF  REINFORCED  CONCRETE 


fire  limits,  superior  to  an  imperfect  structure  in  which  either  a  steel 
frame  is  to  be  found,  or  part  of  which  is  reinforced  concrete.  We 
should  recognize  in  the  beginning  that  all  types  of  construction  for 
financial  reasons  must  be  encouraged.  It  should  be  our  object  only  to 
see  to  it  that  different  types  are  applied  in  the  most  intelligent  man¬ 
ner.  At  your  1907  meeting,  Mr.  W.  J.  Milled  referred  to  this  subject 
when  he  argued  that  a  radical  departure  be  made  in  the  designation 
of  different  types  of  buildings.  He  says  that  structures  should  not 
be  grouped  primarily  in  classes,  but  according  to  type. 

To  emphasize  the  character  of  reinforced  concrete  building  I  sub¬ 
mit  the  following  grouping  for  different  grades  of  construction: 

Type  I.  Buildings  with  a  cage-like  steel  frame  supporting  all  floor 
and  wall  loads;  the  combined  dead  and  live  load  weights  carried 
directly  to  the  foundation  by  the  steel  frame;  all  structural  parts  of 
the  building  built  of  incombustible  materials;  all  projecting  parts 
structurally  anchored  to  the  steel  frame.  In  this  type  reinforced  con¬ 
crete  may  be  used  for  floor  slabs,  partitions,  curtain  walls  and  foun¬ 
dation  footings.  No  beams  or  girders  taking  computed  loads  either  in 
the  floors  or  walls  should  be  of  reinforced  concrete;  they  should  be 
of  structural  steel.  In  heavy  footings  the  reinforcement  should  consist 
of  rolled  I-beam  grillages  instead  of  rods;  for  light  footings  rod  re¬ 
inforcement  should  be  approved. 

Type  II.  Buildings  with  reinforced  concrete  cage  construction;  all 
floor  and  wall  loads,  dead  and  live,  carried  directly  to  the  foundation 
by  the  structural  frame;  all  parts  of  incombustible  materials;  I  refer 
to  floor  slabs,  curtain  walls,  partitions,  etc.;  all  projecting  parts  to  be 
anchored  to  the  frame.  In  this  structure  the  frame,  that  is,  beams, 
girders,  spandrel  wall  girders  and  columns  are  of  reinforced  concrete; 
but  in  larger  buildings  heavy  members  may  be  of  structural  or  rolled 
steel  encased  in  concrete.  Floor  slabs,  curtain  walls,  partitions  and 
footings  are  of  reinforced  concrete.  Normally  every  part  is  of  rein¬ 
forced  concrete. 

Type  III.  Buildings  with  self-supporting  masonry  walls;  walls  car¬ 
rying  adjacent  floor  panels;  structural  steel  or  reinforced  concrete  col¬ 
umns  in  the  interior;  floor  framing  of  structural  steel  or  reinforced 
concrete;  all  important  parts,  such  as  walls,  floor  slabs,  partitions,  of 
incombustible  materials.  This  description  is  intended  to  include  most 
of  the  schemes  of  building  grouped  under  class  B  in  the  1906  San 
Francisco  ordinance.  That  ordinance  included  all  reinforced  concrete 

2Cf.  “Class  ‘A’  Construction  from  the  Standpoint  of  the  Architect  and 
Architectural  Engineer”;  by  W.  J.  Miller;  31st  Annual  Meeting  of  the  Fire 
Underwriters’  Association  of  the  Pacific  Coast;  January  1907;  page  111. 


BUILDINGS  OF  REINFORCED  CONCRETE 


5 


construction  under  class  B.  My  classification  puts  reinforced  con¬ 
crete  cage  construction  into  a  class  by  itself  (see  type  No.  II).  It  is 
an  injustice  to  group  reinforced  concrete  cage  frames  with  buildings 
having  self-supporting  walls. 

Type  IV.  Buildings  with  masonry  walls  supporting  the  adjacent 
floors;  interior  of  floors  supported  by  studded  partitions  or  by  wooden 
or  steel  girders;  combustible  materials  may  be  used  in  all  parts  ex¬ 
cept  for  walls.  Cast  iron  columns  may  be  used  in  this  type.  Walls, 
columns,  important  floor  girders,  footings,  may  be  of  reinforced  con¬ 
crete. 

Type  V.  Mill  construction.  Buildings  of  heavy  timber  frames  and 
floors  with  exterior  walls  and  roof  of  corrugated  iron  fastened  to  tim¬ 
ber  framing  and  without  boarding. 

Type  VI.  Frame  buildings.  These  buildings  may  be  built  entirely  of 
combustible  materials,  except  roofs  for  buildings  within  certain 
described  fire  limits,  as  specified  by  the  city  ordinance. 

Wide  Possibilities  for  Reinforced  Concrete. 

The  range  of  application  for  reinforced  concrete  is  very  wide.  It 
may  be  used  for  details  in  all  six  building  types;  for  footings  in  types 
V  and  VI;  structurally  in  the  first  four  types  for  important  members 
taking  computed  stresses.  It  may  be  wholly  employed  in  type  II.  It 
finds  its  most  important  adaptation  in  types  I  and  II.  It  is  for  these 
two  schemes  of  building,  representing  the  classes  requiring  the  most 
developed  engineering  skill  and  knowledge,  that  the  greatest  care 
must  be  taken  in  designing  reinforced  concrete  parts.  My  later  re¬ 
marks  apply  mainly  to  the  art  and  science  of  reinforced  concrete  build¬ 
ing  for  the  first  two  groups. 

Economy  and  Adaptability  of  Reinforced  Concrete. 

In  their  text  on  Reinforced  Concrete,  theory  and  design,  Messrs. 
Buel  and  Hills  give  a  clear  exposition  of  the  economic  and  practical 
difficulties:  “In  directing  building  work  in  concrete-steel  the  engineer 
has  a  long  list  of  traditions  to  overcome.  Foremen  and  masons  whose 
training  has  been  wholly  in  the  use  of  concrete  as  a  filler  over  brick 
arches  or  trough  sections  of  steel  do  not  readily  perceive  that  a  rein¬ 
forced  concrete  floor  slab  is  a  radically  different  structure  and  must 
be  fabricated  according  to  entirely  different  standards  of  workman¬ 
ship.  To  meet  this  difficulty  the  engineer  has  to  arm  himself  with  a 
rigidly-drawn  specification  and  careful  supervision  and  inspection. 

3Cf.  Reinforced  Concrete;  by  Buel  &  Hill,  second  edition,  p.  387;  pub. 
by  Eng.  News,  1906. 


6 


BUILDINGS  OF  REINFORCED  CONCRETE 


The  requirements  for  materials  and  workmanship  in  concrete-steel  con¬ 
struction  and  the  imperative  necessity  of  enforcing  them  have  been 
discussed  in  a  preceding  chapter.  Negligence  in  these  matters  is  fre¬ 
quently  punished  by  disaster  in  concrete  steel  building  work.” 

These  remarks  apply  particularly  to  San  Francisco  and  some  other 
parts  of  the  Pacific  Coast.  In  California  the  objection  of  labor  to  the 
new  material  and  methods  has  been  peculiarly  pronounced.  Lack  of 
respect  for  new  requirements  has  produced  failures,  but  happily  not 
restricted  to  our  Western  community  A  An  impartial  study  of  these 
failures  will  convince  the  reader  that  the  disastrous  results  were  not 
due  to  a  fault  inherent  in  reinforced  concrete  design,  but  entirely  to 
an  improper  or  unintelligent  use  of  the  combined  materials.  It  would 
be  easy  to  review  cases  of  collapse  for  buildings  with  structural  steel 
frames,  but  no  one  would  think  of  using  such  citations  as  arguments 
to  impute  dangerous  qualities  to  steel  frame  construction."’ 

Pertinent  remarks  for  San  Francisco  conditions  are  made  by  Mr. 
Lewis  A.  Hicks,  a  local  engineer  and  contractor.  He  may  be  consid¬ 
ered  intimately  acquainted  with  California  building  problems;  his 
words  are  quoted  with  emphasis.6  “Before  the  earthquake,  the  efforts 
of  those  interested  in  introducing  this  comparatively  new  material  (re¬ 
inforced  concrete)  had  been  abortive  owing  to  the  active  resistance 
of  persons  interested  in  the  manufacture  of  clay  products,  the  oppo¬ 
sition  of  the  bricklayers’  unions,  and  the  general  inertia  of  the  build¬ 
ing  trades  to  accept  changes  in  long  established  methods  of  construc¬ 
tion.  When  the  pressure  of  this  conservatism  was  removed  by  the 
conditions  following  the  fire,  there  was  a  prompt  reaction  in  the  pub¬ 
lic  mind  in  favor  of  the  indiscriminate  use  of  a  material  that  would 
furnish  greater  security  against  damage  by  earthquake  and  fire  than 
the  brick  construction  formerly  prevailing,  and  without  entailing  the 
excessive  cost  of  a  steel  frame.  For  a  time  it  seemed  as  if  every  build¬ 
ing  put  up  was  to  be  made  of  concrete,  but  a  sufficient  interval  has 
now  elapsed  to  make  it  possible  to  outline  broadly  the  place  in  build¬ 
ing  work  that  it  is  well  adapted  to  take,  as  well  as  such  economic  lim¬ 
itations  as  insure  the  use  of  other  materials  for  certain  purposes.” 

4For  instructive  examples  of  collapsed  buildings  I  may  cite: 

1.  The  Bixby  Hotel  Disaster,  Long  Beach,  California;  cf.  Official  Report 
of  Cement  Workers’  Union;  the  Architect  and  Engineer  of  California  for 
Dec.,  1906,  vol.  VII,  Nos.  1  and  2;  and  Eng.  News,  Vol.  56,  p.  555.  Nov.  29, 
1906. 

2.  Failure  of  Reinforced  Concrete  Buildings  at  Philadelphia;  cf.  Eng. 
News,  Vol.  58,  p.  69,  July  18,  1907. 

3.  Report  on  Failure  of  Reinforced  Concrete  Building  of  Eastman  Kodak 
Co.,  Kodak  Park,  New  York;  cf.  Eng.  News,  Vol.  57,  p.  130,  Jan.  31,  1907. 

5Cf.  The  Collapse  of  a  Building  Under  Construction;  by  H.  de  B.  Par¬ 
sons,  Trans.  Am.  Soc.  C.  E.,  Vol.  53,  p.  1,  Dec.,  1904. 

6Cf.  An  article  entitled,  “Reinforced  Concrete  Construction”;  by  Lewis 
A.  Hicks,  Mining  and  Scientific  Press,  p.  503,  April  20,  1907. 


BUILDINGS  OP  REINFORCED  CONCRETE 


7 


Mr.  Hicks  gives  a  concise  statement  of  his  views  for  building  con¬ 
ditions  in  the  business,  warehouse  and  banking  districts  surrounding 
lower  Market  Street.  He  speaks  of  the  necessary  struggle  to  main¬ 
tain  down-town  property  values  and  points  out  that  the  character  of 
improvement  must  be  determined  largely  by  the  ability  of  the  owners 
to  pay  for  them.  On  the  one  hand,  with  high  lot  values  and  little 
available  funds,  the  owner  selects  a  low  building  of  brick  walls  with 
interior  wood  construction  (see  type  IV).  On  the  other,  with  valuable 
real  estate  and  plenty  of  money,  he  selects  a  steel  frame  building, 
type  I.  To  quote  Mr.  Hicks  again:  “Between  these  two  extremes 
there  are  a  large  number  of  people  owning  valuable  street  frontage 
with  deep  lots  who  must  soon  find  some  commercial  use  for  their 
property  and  who  desire  fairly  permanent  improvements  of  moderate 
height  but  of  class  A  character.”  He  has  in  mind  the  structure  which 
I  describe  as  type  II,  or  possibly  also  type  III,  in  concrete.  “It  is 
among  such  (people)  that  reinforced  concrete  will  find  its  most  ex¬ 
tended  use.”  Further  he  says: 

“These  requisite  conditions  are  most  successfully  fulfilled  by  a 
building  with  reinforced  concrete  frame,  floors,  roofs,  and  curtain  walls, 
with  its  front  veneered  with  stone,  brick,  or  terra  cotta  bonded  into 
concrete  backing,  and  all  its  structural  members  fireproofed  with  a 
secondary  skin  of  metal  furring  and  plaster,  furnishing  protected  air¬ 
spaces.  Such  a  building  is  class  A  in  every  detail  of  construction  and 
in  appearance,  and  in  its  virtual  power  to  resist  fire  and  earthquake 
it  is,  in  my  opinion,  within  the  limit  of  height  considered,  equally  as 
reliable  as  a  steel  frame  structure. 

The  amount  of  concrete  used  in  fireproofing  the  columns,  beams, 
floor  and  roof  of  a  modern  steel  building  is  practically  sufficient  to 
build  the  same  members  in  reinforced  concrete,  and  the  difference  in 
cost  of  the  two  structures  will  be  roughly  the  difference  in  the  weight 
of  steel  used.  The  elimination  of  two-thirds  to  three-quarters  of  the 
steel  required  for  a  steel  frame  is  entirely  practicable,  but  the  saving 
is  not  as  significant  as  would  appear  at  first  glance.  The  cost  of  a 
finished  class  A  structure  will  range  from  four  to  six  times  the  cost 
of  the  steel  frame,  and  the  saving  effected  will  therefore  amount  to 
from  10  to  15  per  cent  of  the  cost  of  the  improvements. 

“Where  the  relation  between  the  value  of  the  ground  and  the  cost 
of  the  building  is  normal,  or  as  one  to  one,  there  follows  that  the 
saving  on  the  entire  investment  amounts  to  from  5  to  7  per  cent.  It 
will  frequently  happen  that  an  owner  will  prefer  to  pay  this  addi¬ 
tional  cost  for  the  sake  of  having  a  type  of  construction  that  has  been 
tested  to  a  finality.  It  is  also  true  that  in  incompetent  hands  this 


8 


BUILDINGS  OF  REINFORCED  CONCRETE 


apparent  saving  of  5  per  cent  may  easily  shrink  to  disappearance  and 
that  time,  apparently  in  favor  of  the  concrete  type,  may  be  wasted 
to  such  an  extent  that  the  steel  frame  will  gain  rather  than  lose  by 
such  a  comparison.” 

Hardly  had  the  San  Francisco  fire  ruins  cooled  when  reinforced  con¬ 
crete  experts,  self-styled,  arose  as  if  from  the  ashes  in  every  quarter 
of  the  city.  Results  show  that  at  least  a  number  of  these  gentlemen 
were  grossly  incompetent  or  careless.  Their  labors  have  been  very 
harmful  to  the  cause  of  reinforced  concrete  construction  in  California. 
In  the  two  years  following  the  conflagration  a  noticeable  setback  was 
given  to  the  selection  of  this  type  of  building;  happily  at  present  there 
are  signs  of  a  recovery  of  confidence.  The  incompetent  or  grossly 
done  work  immediately  after  our  disaster  may  be  divided  into  two 
classes:  1,  work  structurally  safe  but  of  unreasonably  high  cost;  2, 
work  faulty  in  design  or  introducing  unique  or  quack  systems. 

All  structural  members  of  reinforced  concrete  which  take  computed 
stress,  or  which  form  essential  parts  of  a  building  frame,  in  rational 
design  must  be  protected  by  fireproofing  envelopes,  just  as  much  and 
to  nearly  the  same  extent  as  structural  rolled  steel  members  doing 
similar  duty.  Such  envelopes  must  not  take  computed  stresses;  they 
must  protect  the  main  members  from  corrosion  or  fire,  even  though 
they  themselves  are  destroyed  by  heat  or  the  action  of  the  elements. 
Proper  design  whereby  sufficient  protection  is  insured  by  envelopes 
to  main  reinforced  concrete  members  would  prohibit,  in  some  instances 
at  least,  the  use  of  reinforced  concrete  versus  rolled  steel.  This  pro¬ 
hibition  would  be  due  to  cost  or  to  largeness  of  cross  section,  or  both. 
A  case  in  point  would  be  a  main  column  in  the  lower  stories  of  a  high 
building  constructed  wholly  of  reinforced  concrete;  such  columns  ade¬ 
quately  protected  would  often  be  of  unsightly  and  excessive  diameters 
and  would  cost  more  than  equivalent  built-steel  columns. 

In  order  to  make  the  cost  of  reinforced  concrete  buildings  appear 
favorable  to  the  owner  in  comparison  to  steel  frame,  class  A  construc¬ 
tion,  local  designers  and  contractors  (especially  the  contracting  en¬ 
gineers  for  patented  systems)  have  been  tempted  to  propose  designs  of 
excessive  cheapness.  Their  results  have  been  secured  by:  1,  cutting 
down  the  thickness  of  floor  slabs  and  curtain  walls  and  reducing  the 
amounts  of  concrete  wherever  possible;  2,  by  omitting  reinforcement 
steel  where  theoretically  desirable  on  the  ground  that  without  such 
steel  the  building  would  stand  up;  for  example,  metal  for  reverse 
bending  in  columns  and  over  supports  of  continuous  girders,  anchorage 
steel  desired  for  stiffness  and  continuity  of  joints;  3,  the  simplification 
of  forms  by  omitting  knee  braces  between  main  girders  and  columns; 


BUILDINGS  OF  REINFORCED  CONCRETE 


9 


by  omitting  cross  girders  between  columns  (as  in  the  Bixby  hotel), 
or  spandrel  wall  beams;  and,  4,  by  neglecting  requirements  for  fire¬ 
proofing  that  would  be  insisted  upon  by  the  same  designers  in  the 
case  of  alternative  steel  frame  buildings,  arguing  that  the  reinforced 
concrete  type  of  construction  needs  no  special  fireproofing  envelope. 
Were  some  of  these  desirable  conditions  reasonably  satisfied,  the  dif¬ 
ference  in  cost  between  steel  frame  and  reinforced  concrete  designs 
would  and  could  not  be  marked,  even  where  the  designers  and  con¬ 
tractors  are  experts. 

Immediately  after  the  fire  many  professional  men  flocked  to  San 
Francisco.  Some  with  little  experience  proclaimed  themselves  struc¬ 
tural  engineers.  They  were  unfamiliar  with  reinforced  concrete  de¬ 
sign  and  construction;  but  worse,  they  were  not  acquainted  with  local 
costs  and  markets  for  material,  nor  did  they  appreciate  our  peculiar 
labor  conditions.  It  is  not  surprising,  therefore,  that  a  large  number 
of  reinforced  concrete  buildings  were  constructed  which  cost  more 
than  the  first  estimates.  Indeed,  some  notable  structures,  recently 
completed,  have  cost  almost  double  the  originally  stated  figures.  One 
can  hardly  understand  how  otherwise  intelligent  owners  could  allow 
themselves  to  be  misled  or  duped  to  this  extent. 

For  example,  in  one  instance,  an  Eastern  architect  who  combined 
his  designing  office  with  a  contracting  staff,  arranged  to  design  and 
construct  complete  a  hotel  in  reinforced  concrete,  the  lump  sum  to 
be  about  $450,000.  It  was  agreed  that  the  work  should  be  done  upon 
a  percentage  basis,  the  plausible  argument  being  that  the  owner  was 
to  pay  only  the  actual  expenditures  for  labor  and  materials,  plus  a 
percentage  for  the  architect,  to  defray  the  expenses  of  his  office  and 
field  establishments.  A  surprisingly  large  number  of  contracts  were 
let  in  this  way,  with  no  visible  protection  for  the  owner.  The  hotel 
building  just  cited  was  completed  after  great  delays.  I  am  informed 
that  more  than  $750,000  was  expended.  Beside,  who  is  to  pay  the 
owner  for  loss  of  rents  incident  to  the  prolonged  construction? 

In  another  case  a  building  for  office  purposes  planned  with  steel 
frame  (type  I)  was  studied  by  a  competent  engineer  and  upon  his 
design  a  reliable  contractor  offered  to  erect  the  building  complete  for 
a  lump  sum  payment  of  about  $120,000.  A  reinforced  concrete  expert 
who  combined  according  to  his  prospectuses  the  talents  of  architect 
and  contractor  offered  to  build  the  structure  in  reinforced  concrete 
(type  II)  .for  about  $94,000  on  a  percentage  basis,  as  in  the  hotel  case 
just  mentioned.  By  what  seems  almost  hypnotic  influence,  the  owner 
agreed  to  the  second  proposition  with  no  real  security  or  assurance 
that  the  work  could  be  done  at  the  $94,000  figure.  Results  have  shown 


10 


BUILDINGS  OF  REINFORCED  CONCRETE 


that  the  confidence  was  misplaced.  The  building  in  question,  when 
completed,  cost  nearly  $150,000. 

I  might  describe  a  number  of  other  instances  where  buildings  struc¬ 
turally  sound  have  cost  too  much  money.  San  Francisco  owners  have 
been  disgusted  by  these  cases  and  many  of  them  are  loth  to  try  the 
experiment.  Fortunately,  a  goodly  number  of  first-class,  modern  type 
reinforced  concrete  buildings  have  been  brought  to  successful  com¬ 
pletion  at  moderate  prices,  and  it  is  to  be  expected  that  the  attitude 
of  doubt  or  fear  in  the  minds  of  prospective  builders  will  be  dissipated. 

A  number  of  reinforced  concrete  buildings  have  been  completed  in 
the  city  with  unusual  designs.  The  illustrations  (see  figures  1  and  2) 
exhibit  fantastic  reinforcement.  Figure  1  shows  the  floor  and  spandrel 
wall  reinforcement  made  of  straps  meshed  to  form  equilateral  triangles. 
Old  wire  cables  were  introduced  to  reinforce  the  light  latticed  floor 
girders.  The  columns  consist  of  a  mixture  of  light  rods  and  bars  held 
together  by  latticed  bands.  The  designer  claims  for  this  building  a 
great  advantage,  that  the  reinforcement  metal  was  erected  complete 
for  the  entire  structure  before  depositing  concrete.  Indeed,  the  major 
part  of  the  steel  work  was  put  in  place  before  the  concrete  forms  were 
built.  I  do  not  know  the  cost  of  this  building,  but  it  certainly  repre¬ 
sents  an  eccentric  type. 

Figures  3  and  4  deserve  critical  mention;  they  are  views  typical  of 
a  class  of  structures  which  cost  large  amounts  of  money.  One  of  the 
great  sources  of  expense  is  the  unnecessarily  large  amount  of  steel 
reinforcement  for  columns  and  heavy  girders.  It  is  to  be  presumed 
that  the  designers  were  anxious  to  be  on  the  safe  side.  Figures  3  and  4 
give  progressive  views  during  the  placing  of  first-floor  steel.  Note  the 
unusual  amount  of  metal  in  the  columns.  The  slab,  girder,  and  column 
metal  meeting  at  column  bases  is  so  thick  that  there  is  little  room  left 
for  concrete.  A  column  contains  about  sixteen  rods,  each  about  two 
inches  in  diameter.  The  columns  pictured  carry  only  five  stories. 

Mr.  Wm.  H.  Hall?  gives  a  striking  description  of  column  design  in 
eighteen  different  buildings  erected  in  1907.  From  his  table  of  figures, 
his  critical  comparisons  and  his  sketches,  one  may  note  at  a  glance  the 
great  diversity  in  method,  the  utter  lack  of  consistency,  the  wide  va¬ 
riation  in  the  proportions  of  steel  to  concrete  designed  to  effect  sub¬ 
stantially  like  duties.  He  says:  “Viewed  broadly,  the  designing  of 
columns  in  the  reinforced  concrete  constructions  of  San  Francisco  seems 
to  show,  in  some  cases,  either  ignorance  of  what  is  safe,  or  a  determi¬ 
nation  to  save  money  at  the  expense  of  structural  safety;  in  other 

7Cf.  Reinforced  Concrete  Practice  in  San  Francisco — Column  Design; 
by  W.  H.  Hall;  The  Architect  and  Engineer  of  California,  May,  1907. 


BUILDINGS  OF  REINFORCED  CONCRETE 


11 


cases,  ignorance  of,  or  a  lack  of  confidence  in,  what  is  just  right  in 
design,  and  determination  to  be  on  the  safe  side  in  the  matter  of  re¬ 
inforcement  strength,  at  the  sacrifice  of  economy;  in  still  other  cases, 
a  weak  concession  to  the  desire  to  keep  down  sizes  of  interior  columns, 
and  as  a  consequence,  the  reduction  of  concrete  and  increase  of  steel 
to  take  place  in  compression,  until  the  danger  point,  at  the  other 
extreme  of  conditions,  has  been  approached.” 

Typical  of  high-class  reinforced  concrete  work  for  warehouse  con¬ 
struction  is  a  group  of  buildings  built  immediately  after  the  fire  for 
the  A.  Schilling  Company,  wholesale  merchants  for  tea,  coffee,  spices 
and  similar  products.  The  Tea  Building  has  self-supporting  walls  of 
brick,  with  the  interior  columns  and  floors  of  reinforced  concrete.  The 
structure  is  subdivided  into  three  compartments  per  floor  by  two 
brick  cross  or  fire  walls.  The  doorways  leading  through  the  fire  wall 
are  protected  by  double  fire  doors,,  asbestos  lined  and  tin  clad.  All 
windows  are  provided  with  metal  sash  and  frame,  with  wire-glass 
panes.  One  of  the  few  buildings  in  the  Mission  district  before  the 
fire  which  could  compare  with  the  above  description  was  the  California 
Electrical  Works  at  Second  and  Folsom  Streets.  The  interior  of  the 
latter  building,  however,  was  of  timber,  heavy  mill  construction,  and 
therefore  inflammable.  Buildings  like  the  Schilling  Building  are  now 
common  in  the  city.  Indeed,  a  large  number  of  the  later  ones  built 
are  true  reinforced  concrete  structures  in  that  their  walls  are  not 
self-supporting  but  are  carried  upon  a  frame-work.  Some  of  the  re¬ 
cent  reinforced  concrete  warehouses  have  gone  up  in  record  time;  an 
excellent  example  is  the  warehouse  building  for  the  Tillman  Bendel 
Company,  designed  according  to  the  Kahn  System. 

Exorbitant  amounts  of  metal  in  the  lower  story  columns  of  reinforced 
concrete  buildings  is  a  common  fault  in  a  number  of  the  first  buildings 
erected  in  San  Francisco.  The  buildings  to  be  so  criticised  are  from 
five  to  eight  stories  in  height.  The  designers  were  anxious  to  get  suffi¬ 
cient  strength.  It  is  a  fact  that  in  at  least  one  of  these  structures 
there  was  relatively  a  dearth  of  continuity  steel  to  take  reverse  bend¬ 
ing  moment  in  the  upper  sides  of  beams  and  girders.  To  reduce  the 
cost  of  forms  many  designers  omitted  knee  brace  connections  between 
columns  and  floor  beams.  One  can  not  deny  that  buildings  with  these 
deficiencies  may  never  show  signs  of  weakness;  but  such  practice  is 
to  be  deplored  in  a  community  which  has  been  subjected  recently  to  a 
severe  earthquake  shock.  To  save  3  per  cent  in  the  total  structural 
cost  of  a  building  vitally  important  structural  features  are  omitted. 
It  would  be  better  to  save  the  3  per  cent  by  omitting  unnecessary 
architectural  decorations.  I  might  add  maliciously  that  this  could 


12 


BUILDINGS  OF  REINFORCED  CONCRETE 


have  been  done  with  great  effect  in  one  building,  which  has  been 
loudly  decorated  in  glaring  tile  of  all  colors  of  the  rainbow. 

For  the  California  Market  a  one-story  structure  or  shed  was  re¬ 
cently  built  of  reinforced  concrete,  and  is  worthy  of  comment.  The 
building  consists  of  a  series  of  reinforced  columns  supporting  roof 
trusses  of  the  same  materials.  The  framing  is  similar  to  that  of  a 
typical  steel  mill  building.  The  result  is  a  number  of  sheds  paralleling 
each  other.  The  designer  is  a  man  versed  in  reinforced  concrete, 
whose  schooling  and  experience  were  obtained  in  continental  Europe. 
Small  framed  roof  trusses  of  reinforced  concrete  are  at  present  not 
uncommon  in  France  or  Germany;  but  with  our  California  conditions, 
especially  the  high  price  of  labor,  I  think  it  would  have  been  more  ap¬ 
propriate  to  use  light  steel  trusses.  Reinforced  concrete  can  not  be 
used  to  fit  every  situation.  I  believe  this  is  a  case  where  it  would 
have  been  better  not  to  have  used  the  material. 

Again,  designs  in  reinforced  concrete  prepared  by  an  engineer  not 
thoroughly  conversant  with  economic  construction  are  very  apt  to 
combine  features  distinctive  of  a  number  of  the  so-called  patented 
systems  with  an  unnecessary  complication  of  parts.  It  is  not  surprising 
to  the  writer  to  find  that  buildings  constructed  in  this  patch-quilt  man¬ 
ner  have  cost  from  30  per  cent  to  50  per  cent  more  than  equivalent 
designs  prepared  according  to  first  principles.  A  case  of  a  hotel 
recently  came  to  the  writer’s  attention  where  the  high  estimated  cost 
was  due  mainly  to  uneconomic  proportions  for  floor  panels  contem¬ 
plating  20-foot  square  slabs,  with  an  unintelligent  placing  of  reinforce¬ 
ment  metal,  proposing  reinforcement  in  two  directions.  The  original 
designs  were  discarded.  The  revised  plans  changed  the  floor  propor¬ 
tions,  substituted  a  ribbed  floor  with  thin  slabs  reinforced  in  one 
direction  only  and  reduced  the  contractor’s  bid  in  the  ratio  of  3  to  2. 

Conclusions — Regarding  Economy  and  Adaptability. 

Concrete  buildings  of  the  most  developed  type,  No.  II,  in  my  table 
must  be  considered  as  worthy  of  classification  with  first-class  steel¬ 
framed  structures.  They  require  the  same  degree  of  structural  talent 
in  the  preparation  of  specifications  and  plans  and  in  the  field  inspec¬ 
tion  and  methods  of  erection.  A  building  consisting  wholly  in  struc¬ 
tural  parts  of  reinforced  concrete,  however,  should  not  be  built  for 
great  heights.  The  San  Francisco  ordinance  wisely  limited  the  heights 
of  such  structures  to  eight  stories.  I  should  prefer  to  limit  them  to 
six  stories,  because  I  believe  above  that  height  the  steel  frame  build¬ 
ing  is  the  more  logical.  For  buildings  over  six  stories  the  columns  in 
the  lower  floors  would  become  excessively  heavy  when  designed  in 


BUILDINGS  OF  REINFORCED  CONCRETE 


13 


reinforced  concrete.  Buildings  have  been  built  in  San  Francisco  and 
Los  Angeles  where  reinforced  concrete  first-story  columns  actually 
cost  more  than  equivalent  members  of  structural  steel  encased  in  fire¬ 
proofing  of  concrete;  because  the  architect,  and  in  one  instance  the 
owner  also,  approved  of  the  extra  cost  merely  to  he  able  to  say 
that  there  was  no  structural  steel  in  the  building.  Advocates  of 
reinforced  concrete,  in  their  zeal  to  exploit  or  defend  its  methods,  have 
argued,  unwisely  I  think,  that  buildings  of  greater  height  than  eight 
stories  should  be  erected  in  reinforced  concrete.  That  higher  struc¬ 
tures  can  be  built  I  readily  admit.  The  McGraw  Building,  eleven 
stories,  in  New  York  City;  the  Gloekler  Building,  ten  stories,  in  Pitts¬ 
burg;  the  Ingalls  Building,  fifteen  stories,  in  Cincinnati,  are  examples.8 

Discussing  his  design  of  the  McGraw  Building,  Mr.  Burr,  referring 
to  comments  from  other  engineers,  says:  “Instances  of  bad  design, 
worse  fabrication  and  marked  unfamiliarity  with  concrete  work  have 
been  exhibited  to  illustrate  the  difficulties  attending  the  construction 
of  reinforced  concrete  work  and  its  alleged  uncertain  character.  It  is 
probably  fully  understood  among  experienced  and  well-informed  en¬ 
gineers,  as  has  been  often  stated,  that  the  degree  of  ability  necessary 
in  the  design  of  a  reinforced  concrete  structure,  the  thoroughness  of 
inspection,  and  the  care  in  fabrication,  are  neither  less  nor  more  than 
required  in  the  best  quality  of  structural  steel  work.  In  fact,  in  these 
respects,  it  may  be  reasonably  maintained  that  both  classes  of  con¬ 
struction  are  in  the  same  category.  To  cite  badly-designed  and  badly- 
handled  concrete  work  as  an  argument  against  first-class  reinforced 
concrete  construction  is  precisely  like  citing  unscrupulously-designed 
and  badly-built  back-country  highway  bridges  of  poor  steel  as  a  legiti¬ 
mate  argument  against  first-class  structural  steel  work.  The  proper 
question  is,  What  can  be  done  with  competent  design  and  first-class 
materials  and  work?  not,  What  defects  can  be  developed  by  bad 
material  and  inefficiency  of  handling? 

From  what  precedes  I  assume  that  it  is  amply  shown  that  in  type 
II,  reinforced  concrete  has  its  full  development,  and  that  it  has  come 
to  stay  as  a  permanent  form  of  construction,  despite  the  fact  that  it 
has  still  to  overcome  many  defects  of  construction  and  many  preju¬ 
dices. 


8The  Reinforced  Concrete  Work  of  the  McGraw  Building;  by  W.  H. 
Burr;  Trans.  Am.  Soc.  C.  E.,  Vol.  60,  p.  443,  June,  1908. 

The  Ingalls  Building;  by  Messrs.  Elzner  and  Anderson;  The  Architec¬ 
tural  Record,  June,  1904.  See  also  The  Eng.  Record,  Vol.  47,  p.  540,  May 
23,  1903. 

A  Ten  Story  Reinforced  Concrete  Building  for  the  Bernard  Gloekler  Co.; 
Eng.  News,  Vol.  58,  p.  488.  Nov.  7,  1907. 


14 


BUILDINGS  OF  REINFORCED  CONCRETE 


It  is  further  to  be  noted  that  in  types  I,  III  and  IV  of  my  list, 
important  parts  may  be  of  reinforced  concrete;  such  parts  as  columns, 
curtain  walls,  floor  slabs,  footings,  according  to  the  particular  type  of 
building  under  construction.  In  the  design  and  erection  of  these 
parts  the  same  degree  of  engineering  skill  and  ability  must  be 
employed  as  in  case  of  type  II. 

Consequently  in  what  follows  I  offer  a  number  of  important  condi¬ 
tions  which  should  influence  the  proportions  of  frames  and  the  details 
of  parts.  I  outline,  in  fact,  salient  features  or  specifications  for  rein¬ 
forced  concrete  design  and  construction  without  undue  emphasis  on 
technical  phraseology.s 

Specifications. 

The  various  elements  of  building  construction  relating  to  reinforced 
concrete  design  may  be  grouped  under  the  following  heads:  1,  floor 
and  slab  roofs;  2,  beams  and  girders  for  roofs  or  floors;  3,  spandrel 
wall  girders;  4,  columns;  5,  foundation  footings;  6,  spandrel  or  curtain 
walls;  7,  partitions  and  other  interior  construction.  The  reinforced 
arch,  culvert,  truss  and  other  complex  forms  do  not  naturally  appear 
in  connection  with  building  construction,  and  therefore  need  not  be 
considered.  Retaining  walls  of  counterfort  types  are  commonly 
designed  in  connection  with  buildings. 

Slabs,  Beams  and  Girders  for  Floors  and  Roofs. 

Reinforced  floor  or  roof  slabs  in  buildings  of  type  I  are  supported 
on  structural  steel  beams  and  girders.  Desirable  slab  spans  range 
from  6  ft.  to  8  ft.  Such  slabs  also  occur  in  type  III.  In  type  II  floor 
slabs  are  supported  on  reinforced  concrete  beams  and  girders  instead 
of  on  structural  steel.  For  this  case  I  should  limit  spans  from  6  to  8 
ft.  also;  that  is  to  say,  I  recommend  in  all  types  what  may  be  termed 
a  ribbed  roof  or  floor.  The  beams  and  girders  in  types  I,  II,  III,  for 
economy  and  architectural  conditions,  will  usually  range  in  span  from 
12  to  20  ft.,  rarely  25  ft.  as  a  maximum.  I  should  prefer  in  general  to 
see  the  limit  of  panels  20  ft.  square;  that  is,  columns  spaced  not  to 
exceed  20  ft.  In  some  types  of  floor  design,  notably  the  mushroom 
system  devised  by  C.  A.  P.  Turner, io  the  slabs  are  not  ribbed,  but 
are  of  constant  thickness  for  the  complete  panel  marked  by  column 
centers.  Other  things  being  equal,  I  consider  this  type  of  floor  less 
stiff  than  a  ribbed  floor. 

9For  a  comprehensive  list  of  reinforced  concrete  buildings  in  course  of 
construction  in  San  Francisco,  1907,  consult:  “The  Rebuilding  of  San 
Francisco — Reinforced  Concrete  Buildings”;  by  W.  H.  Hall;  The  Archi¬ 
tect  and  Engineer  of  California,  Vol.  9,  p.  61,  July,  1907. 

ioCf.  Principles  of  Reinforced  Concrete  Construction;  by  F.  E.  Turneaure 
and  E.  R.  Maurer;  2nd  ed.,  1909;  p.  328. 


BUILDINGS  OP  REINFORCED  CONCRETE 


15 


In  designing  floor  slabs  of  medium  or  short  spans,  say,  less  than  8 
ft.,  the  formula  for  bending  moment  should  be  for  uniform  loads, 

Tvr=^-  For  longer  spans  the  interior  slabs  of  a  floor  plan  should 
1  x  12 

be  designed  by  the  same  formula,  but  outer  or  edge  slabs,  which  are 
naturally  less  rigidly  held  at  the  wall  ends,  should  be  designed  for  a 


pi  2 

bending  moment,  M  In  these  formulae  p  —  the  uniform  load 

in  lbs.  per  sq.  ft,  1  —  the  span  length  in  ft.;  M  the  bending  moment 
in  ft.  lbs.  In  all  cases  the  width  of  slab  under  design  is  12  in.  For 
conservative  design,  disregarding  lengths  of  spans,  it  is  customary,  for 

simplicity  and  uniformity,  to  use  in  all  cases  the  formula.  M  = 

though  this  procedure  will  give  slightly  greater  strength  than  neces¬ 
sary  and  greater  cost  for  the  floors. 

I  do  not  advocate  calculations  for  slabs  assumed  supported  on  all 
four  sides,  and  doubly  reinforced;  that  is,  reinforced  with  two  groups 
•of  bars  at  right  angles.  For  large  slabs  without  beam  ribs,  double 
reinforcement  is  necessary;  also  in  special  systems,  for  example,  the 
mushroom  system  of  Turner,  which  requires  a  radical  arrangement  of 
bars.  In  no  case  should  double  reinforcement  be  used  for  rectangular 
slabs;  such  a  design  is  not  economic.  Where  slabs  are  reinforced  in 
two  directions  they  should  be  square.  The  reinforcement  should  be 
of  equal  amount  in  the  two  directions.  It  should  be  calculated  on  the 
assumption  that  half  the  load  is  carried  by  each  system  of  reinforce¬ 
ment.  The  concrete  is  proportioned  for  only  one  system  or  one-half 
the  load,  as  the  compressive  stresses  in  the  concrete,  due  to  the  two 
systems,  are  at  right  angles  to  each  other,  and  it  may  be  assumed 
that  the  stresses  in  one  direction  do  not  weaken  the  concrete  with 
respect  to  the  stresses  in  the  other  direction.  Square  slabs  are  usually 
designed  for  uniformly  distributed  loads,  resulting  in  an  equal  spacing 
of  rods  throughout  the  slab.  More  exact  analysis  for  the  stresses 
would  lead  to  the  conclusion  that  rods  should  be  spaced  closer  in  the 
central  part  of  the  panel  than  at  the  edges.  The  reinforcement  in  one 


direction  should  be  calculated  for  a  bending  moment,  M  =  kL: 

20 

where  p  is  the  total  load  per  sq.  ft.  on  the  slab. 

In  floor  slabs,  to  prevent  cracks  running  parallel  to  the  main  rein¬ 
forcement,  only  one  system  of  bars  being  used,  some  longitudinal 
reinforcement  should  be  provided.  For  close  beam  spacing,  say  6  ft., 
longitudinal  bars  are  hardly  needed.  For  wider  beam  spacing  their 
need  is  more  important.  The  amount  of  longitudinal  steel  is  a  matter 
of  judgment  and  experience.  The  use  of  in.  to  %  in.  bars  spaced 


16 


BUILDINGS  OF  REINFORCED  CONCRETE 


about  24  in.  is  common  practice,  the  heavier  bars  for  heavier  floors. 
Of  course,  longitudinal  reinforcement  is  unnecessary  in  square  slabs 
reinforced  in  two  directions. 

Floor  slabs  should  not  be  less  than  3 y2  in.  in  total  thickness.  For 
ribbed  floors,  with  slab  spans  about  6  ft.,  the  thickness  will  usually 
range  from  4  to  5  inches,  depending  upon  the  live  loads  specified.  The 
thinner  the  floor  slabs  the  more  care  must  be  taken  in  placing  the 
reinforcement  steel,  particularly  the  steel  over  supports  for  reverse 
bending  moment.  In  thin  slabs  lack  of  precaution  in  placing  steel  is 
a  fruitful  cause  for  ultimate  sagging  of  the  floor.  Not  only  must  the 
steel  be  accurately  placed,  but  it  must  be  kept  in  its  intended  position 
during  the  pouring  and  setting  of  the  concrete.  In  slabs  reinforcing 
steel  never  should  be  nearer  than  y2  in.  to  the  concrete  surface. 

Recently  I  had  occasion  to  examine  carefully  the  structural  parts 
of  a  large  reinforced  concrete  warehouse  and  factory  located  in  San 
Francisco.  The  floor  slabs  are  approximately  18  ft.  square,  supported 
on  four  sides,  and  reinforced  in  two  directions.  They  are  7  in.  thick. 
The  steel  in  the  center  of  the  slab  is  within  y2  in.  of  the  bottom  sur¬ 
face  of  the  concrete.  But  at  the  supports,  though  bent  upward  for 
reverse  bending  moment  on  all  four  sides,  the  bars  do  not  reach  within 
2 y2  in.  of  the  top  surface.  This  is  partly  to  be  explained  by  the  fact 
that  the  top  dressing  of  mortar  is  about  2  in.  thick.  In  almost  all 
cases  these  slabs  have  sagged  and  show  considerable  cracking.  I 
offer  this  example  to  show  how  easily  reinforced  concrete  designs  may 
get  into  bad  repute.  The  sags  and  cracks  in  these  floors  are  a  source 
of  inconvenience  to  the  owners  of  the  building.  Had  the  steel  been 
placed  more  effectively  so  that  at  the  supporting  edges  it  came  within 
%  in.  instead  of  2  y2  in.  of  the  top  surface,  the  slabs  would  have  been 
much  stiffer.  As  it  is,  the  7  in.  slabs  are  really  no  stronger  or  stiffer 
than  5  in.  slabs,  and  carry  an  extra  weight  of  top  dressing.  There  is 
no  reason  why  the  top  dressing  should  be  more  than  %  in.  to  1  in. 
in  thickness.  Further,  had  these  slabs  been  built  of  the  ribbed  type 
with  4  in.  floor  slabs  supported  on  reinforced  concrete  beams,  by  fram¬ 
ing  auxiliary  beams  into  the  square  panels,  a  much  greater  stiffness 
could  have  been  obtained  with  practically  no  change  in  the  amount 
of  materials  and  with  little,  if  any,  extra  cost. 

In  slabs,  beams  and  girders  the  compressive  stress  in  the  concrete 
should  not  exceed  500  lbs.  per  sq.  in.  For  main  reinforcement  steel 
I  should  recommend  deformed  bars  of  a  medium  grade  of  steel  with 
an  elastic  limit  about  40,000  lbs.  per  sq.  in.;  percentage  of  final 
stretch  not  less  than  22  per  cent.  I  should  always  recommend  that 
steel  for  reinforcement  pass  a  bending  test;  that  is,  that  it  be  required 


BUILDINGS  OF  REINFORCED  CONCRETE 


17 


to  bend  cold  180  deg.  over  a  bar  of  its  own  diameter  without  showing 
injury  on  the  outside  of  the  bend.  It  is  a  mistake  to  specify  high 
carbon  steel  or  steel  manipulated  in  the  shops  to  give  higher  ultimate 
resistance  and  elastic  limit.  Higher  values  are  secured  at  the  expense 
of  ductility  and  toughness.  Where  steel  must  bend  to  forms,  par¬ 
ticularly  for  anchorage  purposes,  where  it  must  bend  to  angles  of  90 
deg.  or  less,  a  high-strength  steel  is  more  apt  to  be  injured  than  a 
medium  or  soft  variety.  In  columns  the  steel  can  not  be  stressed  more 
than  about  fifteen  times  the  allowable  stress  in  the  concrete;  there¬ 
fore  not  more  than  about  15x600 — 9000  lbs.  per  sq.  in.  Clearly,  for 
columns,  there  is  nothing  to  be  gained  by  specifying  a  steel  with  elas¬ 
tic  limit  exceeding  40,000  lbs.  per  sq.  in.  In  slabs,  beams  and  girders 
the  futility  of  higher  strength  steel  can  not  be  so  clearly  stated.  Most 
ordinances  specify  that  the  steel  in  beams  and  slabs  shall  be  stressed 
to  16,000  lbs.  per  sq.  in.,  or  to  about  that  value.  One  ordinance  uses 
the  phrase,  “to  one-third  the  elastic  limit. ”n  This  is  a  careless  speci¬ 
fication,  since  it  encourages  the  use  of  high  elastic  limit  steel.12  in 
conservative  specifications  which  limit  the  working  stress  to  16,000 
lbs  per  sq.  in.  there  is  nothing  to  be  gained  by  using  a  steel  stronger 
than  medium  grade.  It  is  curious  to  observe  that  in  a  number  of 
recent  constructions  in  San  Francisco  architects  have  insisted,  with¬ 
out  good  judgment,  upon  specifying  high  elastic  limit  and  have  re¬ 
jected  metal  which  did  not  give  it.  The  metal  was  promptly  removed 
by  the  contractor  to  his  shops,  cold  twisted,  a  process  which  has  long 
been  known  to  increase  the  ultimate  resistance  and  elastic  limit,  and 
as  promptly  returned  to  the  building  and  accepted  by  the  architect. 
This  manipulation  at  the  same  time  decreases  the  percentage  of  final 
stretch  and  contraction  and  injures  the  toughness  in  bending.  The 
metal  has  lost  desirable  qualities  of  ductility  for  undesirable,  not 
needed,  greater  strength. 

In  most  building  ordinances  it  is  prescribed  that  reinforced  con¬ 
crete  girders  be  designed  as  though  they  were  simply  supported.  The¬ 
oretically,  then,  no  steel  would  be  required  over  the  supports  in  the 
concrete  at  the  upper  side  of  the  beam.  Practically,  reinforced  con¬ 
crete  construction  must  be  considered  continuous  over  the  supports, 
and  if  reverse  bending  moment  steel  is  not  provided,  cracks  will 
occur.  The  conservative  rule  for  reverse  bending  moment  steel  is  to 
prescribe  an  equal  amount  of  metal  over  the  supports  to  that  required 

nCf.  The  Building  Law  of  the  City  and  County  of  San  Francisco,  1906, 
section  168. 

i2This  tecnical  point  was  one  of  the  real  questions  at  issue,  but  overlooked 
by  non-technical  judges,  in  the  hearing,  May,  1909,  before  the  Mayor  of 
San  Francisco,  re  the  County  Infirmary  Building. 


18 


BUILDINGS  OF  REINFORCED  CONCRETE 


at  the  center  of  a  span  for  bending  moments  defined  in  an  earlier 
paragraph. 

For  heavy  beams  and  girders  web  reinforcement  must  be  consid¬ 
ered.  In  thin  floor  slabs,  spans  not  exceeding  6  ft.,  stirrups  are  un¬ 
necessary.  It  is  sufficient  to  bend  a  portion  of  the  bars  upward  near 
the  quarter  points.  For  beams  and  girders  a  number  of  the  main 
reinforcement  rods  should  be  bent  up  at  successive  points  near  the 
quarter  of  the  span  so  as  to  provide  diagonal  bars  through  the  web 
at  intervals  near  the  abutment.  Beside  this,  diagonal  reinforcement 
stirrups,  usually  in  vertical  planes,  should  be  introduced.^ 

It  is  common  observation  to  note  in  San  Francisco  today  the  use 
of  reinforced  concrete  in  buildings  of  types  III  and  IV  where  the 
designers  have  used  working  stresses  in  steel  and  concrete,  so  high  that 
they  are  seriously  prohibitive  from  a  conservative,  safe,  point  of  view. 
Recently  I  had  occasion  to  check  the  structural  design  for  a  building 
already  erected  for  automobile  interests,  in  which  stresses  in  con¬ 
crete  and  steel  may  easily  be  double  the  values  prescribed  by  the 
San  Francisco  ordinance.  These  bold  departures  from  usual  practice 
are,  of  course,  due  to  the  desire  to  decrease  the  cost  of  the  structure. 
I  have  heard  engineering  contractors  boast  that  they  were  able  to 
build  on  Market  Street  a  store  and  garage  building  in  reinforced  con¬ 
crete  .  cheaper  than  a  first-class  mill  constructed  building  of  timber. 
The  reason  for  this  is  that  in  the  reinforced  concrete  structure  as 
built,  the  designers  unwisely  provided  excessively  long  spans  and 
improperly  allowed  calculations  based  on  the  use  of  abnormally  high 
and  unsafe  working  stresses.  It  would  be  interesting  to  inquire  why 
we  have  a  building  ordinance  when  nobody  necessarily  follows  its 
prescriptions. 

Design  of  Columns. 

Six  years  ago  our  ideas  on  the  design  of  reinforced  concrete  col¬ 
umns  were  imperfect,  not  to  say  hazy.  Considere  has  just  published 
his  investigations  for  the  strength  and  elasticity  of  hooped  columns. 
it  was  confidently  expected  then  that  hooped  columns  could  be  loaded 
far  above  plain  concrete  pillars;  that  is  to  say,  with  stresses  approach¬ 
ing  1000  to  1200  lbs.  per  sq.  in.  Much  difference  of  opinion  still 
exists  as  to  the  proper  percentage  of  longitudinal  and  hooping  steel 
to  be  used.  Certainly  working  stresses  in  the  concrete  should  not 

i3An  excellent  discussion  of  web  reinforcement  is  given  in:  Principles  of 
Reinforced  Concrete  Construction;  by  Turneaure  and  Maurer,  2nd  ed.,  1909; 
Arts.  86-90,  124-126. 

i4Cf.  Experimental  Researches  on  Reinforced  Concrete;  by  A.  Considere; 
translated  from  the  French  by  L.  S.  Moisseiff;  1903. 


BUILDINGS  OF  REINFORCED  CONCRETE 


19 


exceed  500  lbs.  per  sq.  in.  for  unhooped  columns,  or  700  lbs.  for  those 
with  spiral  or  banded  hoops. 

Column  longitudinal  rods  should  be  tied  by  horizontal  hoops  not 
less  than  *4  inch  in  diameter,  spaced  not  more  than  24  inches.  The 
heavier  the  column  the  more  should  the  bands  increase  in  size  and 
decrease  in  spacing.  The  pitch  of  spiral  hooping  should  not  exceed 
one-seventh  to  one-tenth  the  hoop  diameter. 

Analysis  shows  that  purely  for  theoretical  economy  the  use  of 
longitudinal  steel  in  columns  is  unwarranted.  This  is  an  argument 
in  favor  of  structural  steel  columns  coated  with  concrete  as  a  fire¬ 
proofing.  But  when  reinforced  concrete  columns  are  to  be  used  they 
must  contain  longitudinal  steel  for  practical  strength  requirements. 
Where  reinforced  concrete  columns  are  employed  percentages  of  longi¬ 
tudinal  steel  should  not  exceed  5  per  cent  to  6  per  cent  of  the  con¬ 
crete  area  enclosed  by  the  hooping.  There  are  in  San  Francisco 
buildings  whose  first  story  columns  contain  from  7  per  cent  to  21  per 
cent  of  longitudinal  rods;  that  is,  ratio  of  metal  cross  section  to  con¬ 
crete  area  within  bands.  Hooping  should  never  be  omitted.  Recent 
tests  show  that  its  actual  effect  in  increasing  the  ultimate  carrying 
capacity  of  a  column  is  far  less  than  its  beneficial  effects  regarding 
deformation.  The  chief  object  of  hooping  is  to  increase  the  toughness 
or  ductility  of  concrete  columns.  Hooping  in  combination  with  longi¬ 
tudinal  steel  increases,  so  to  speak,  the  elasticity  of  the  column  with¬ 
out  greatly  enlarging  its  safe  carrying  capacity.  By  toughening  the 
member  it  makes  hooped  columns  much  more  reliable  and  much  safer 
and  saner  parts  of  a  building  frame  of  height  and  weight.  It  must  be 
observed  that  practical  efficiency  and  toughness  can  only  be  gained 
by  hooping  in  combination  with  longitudinal  steel. 

In  buildings  over  five  stories  in  height  usually  it  is  to  be  observed 
that  the  columns  of  the  first  floor  have  large  percentages  of  longi¬ 
tudinal  steel.  This  is  caused  by  the  necessity  of  keeping  diameters 
of  columns  small  so  as  not  to  obstruct  the  floor  space  unduly.  There 
are  numerous  examples  of  buildings,  erected  in  San  Francisco  imme¬ 
diately  after  the  fire,  in  which  excessive  amounts  of  longitudinal  steel 
have  been  used;  indeed,  sufficient  amounts  almost  to  build  the  col¬ 
umns  of  structural  or  rolled  steel  members. 

Too  little  attention  has-been  paid  in  design  to  the  effect  of  eccentric 
loads  on  columns,  particularly  for  columns  which  support  floor  slabs 
and  girders  which  are  themselves  symmetrical.  It  is  entirely  possible 
that  floor  panels  tributary  to  a  column  will  be  unequally  loaded. 
In  warehouses  the  inequality  of  live  loading  may  be  great;  for  instance, 
the  panel  on  one  side  may  be  fully  loaded  while  that  on  the  other 


20 


BUILDINGS  OF  REINFORCED  CONCRETE 


carries  no  live  load  at  all.  Such  conditions  will  throw  bending 
moments  upon  the  columns  and  also  upon  the  floor  girders.  In 
a  high  building  of  small  plan  dimensions  in  one  direction  the  effect 
of  wind  or  other  lateral  forces  may  impose  upon  the  floor  girders  and 
columns  still  larger  bending  stresses  akin  to  those  produced  by 
eccentricity  of  floor  loading.  In  some  columns  and  girders  eccentric 
loading  of  necessity  occurs,  even  for  the  dead  weight;  for  example, 
where  projecting  balconies  and  cornices  are  supported  by  wall  col¬ 
umns.  In  arranging  the  reinforcement  steel  for  columns  and  girders 
in  these  cases  intelligent  application  of  mechanical  principles  for 
design  must  be  observed,  particularly  in  regard  to  so-called  reverse 
bending  moment  metal. 

Bond  of  Concrete  Steel. 

Bond  stresses  should  be  considered  especially  in  connection  with 
the  overlapping  of  main  reinforcement  bars  for  beams  and  columns. 
Tests  show  that  the  ultimate  bond  strength  between  plain  steel  bars 
and  concrete  ranges  from  200-250  lbs.  per  sq.  in.  of  surface  of  contact. 
A  working  bond  stress  of  75  lbs.  per  sq.  in.  is  a  usual  specification. 
For  approved  forms  of  deformed  bars,  bars  which  provide  a  positive 
grip  when  imbedded  in  concrete,  a  safe  working  bond  stress  of  150 
lbs.  per  sq.  in.  may  be  assigned.  A  plain  round  bar  to  develop  its  full 
strength  and  insure  safe  bond  working  stresses  should  be  imbedded 
in  concrete  for  a  length  not  less  than  62y2  diameters;  a  deformed  bar 
not  less  than  about  25  diameters.  These  figures  indicate  to  what 
extent  bars  should  overlap  so  that  they  may  transmit  safely  their  full 
working  stress.  For  anchor  bars  in  addition  to  the  bond  capacity  it 
is  well  to  secure  additional  safety  by  bending  the  bars;  or  where  short 
anchorage  distances  only  can  be  secured,  lugs  may  be  bolted  or 
screwed  to  the  bars. 

Concrete  Shear. 

The  average  ultimate  shearing  strength  of  concrete,  as  observed  in 
beams  having  no  web  reinforcement,  may  be  taken  at  about  100  lbs. 
per  sq.  in.,  calculated  for  the  whole  cross  section.  It  is  best  not  to 
assign  a  working  shear  stress  in  plain  concrete  of  more  than  30  lbs. 
per  sq.  in.  Where  the  webs  of  beams  are  properly  reinforced  with 
inclined  bars  and  stirrups  the  allowable  working  shearing  stress  may 
be  taken  as  high  as  100  lbs.  per  sq.  in.  The  calculation  for  web  rein¬ 
forcement  is  not  a  simple  matter,  as  it  is  based  in  theory  upon  some¬ 
what  difficult  analysis.  An  excellent  exposition  for  the  calculation 
of  web  reinforcement  is  given  in  Turneaure  and  Maurer’s  Principles 
of  Reinforced  Concrete  Construction,  second  edition,  pp.  219-227. 


BUILDINGS  OF  REINFORCED  CONCRETE 


21 


In  heavy  work  designs  often  may  be  criticised  for  crowding  steel 
bars  too  close  together.  The  most  common  cases  are  the  tension 
flange  of  long  slender  girders  and  first-story  columns  in  high  build¬ 
ings.  When  bars  are  massed  they  reduce  the  monolithic  action  of  the 
concrete,  a  very  unfortunate  effect.  The  larger  the  stone  used  for 
concrete  the  larger  should  be  the  minimum  clear  spacing  of  rods.  The 
clear  spacing  of  reinforcing  bars  should  never  be  less  than  one  inch 
when  using  %-inch  stone,  nor  l1/^  inch  when  using  1-inch  stone. 

Forms  for  Concrete  Members. 

The  practical  success  of  reinforced  concrete  work  depends  as  much 
upon  the  intelligent  design  of  forms  as  upon  any  other  factor.  The 
forms  must  be  simple,  easily  removable,  and  so  far  as  possible  should 
be  used  more  than  once.  In  buildings  of  many  stories  this  remark 
applies  particularly  to  the  forms  for  floors  and  columns.  Roughly,  the 
cost  of  forms  may  be  placed  at  30  to  40  per  cent  of  the  total  cost  of 
concrete  in  place.  Buel  and  Hill,  page  388,  give  instructive  prices 
and  conclude  as  follows:  “Experience  on  about  thirty  buildings  shows 
that  it  is  rarely  possible  to  furnish  the  centering  and  remove  it  for 
much  less  than  $4.00  per  cubic  yard,  and  that  only  by  very  bad  man¬ 
agement  or  under  unfavorable  circumstances  can  the  cost  exceed 
$6.00  per  cubic  yard.” 

Forms  must  be  designed  of  sufficient  strength  and  rigidity  to  sup¬ 
port  the  concrete  and  any  other  loads  that  may  be  put  upon  them, 
for  at  least  thirty  days  after  placing  the  concrete.  Forms  must  be  so 
arranged  that  they  are  readily  accessible  for  inspection.  They  must 
not  warp  or  bulge,  due  to  moisture  or  from  the  lateral  pressure  of 
fluid  concrete.  They  must  be  water  tight  so  that  the  concrete  will  not 
lose  water  needed  for  crystallization  or  any  of  the  finer  cement  fluid 
upon  which  the  final  strength  of  the  hardened  mixture  depends.  Forms 
must  be  laid  to  line  and  grade;  they  require  expert  carpenter  work 
and  careful  inspection  from  the  foreman  and  engineer.  Forms  must  be 
cleaned  of  rubbish  before  pouring  concrete.  The  surface  of  lumber 
must  fit  the  requirements  of  finish;  the  finish  desired  also  affects  the 
specification  for  oiling  forms.  Forms  should  not  be  removed  from  the 
under  side  of  floor  or  roof  slabs  in  less  than  two  weeks,  and  preferably 
should  remain  for  still  longer  periods.  The  shores  under  beams  and 
girders  should  be  removed  later  than  the  forms  for  the  adjacent 
slabs.  Column  forms  ought  always  to  be  removed  and  the  concrete 
strength  of  columns  inspected  before  the  supports  are  taken  from 
beams  and  girders.  Forms  should  remain  longer  in  place  in  winter 
than  in  summer.  Important  reinforced  concrete  members  should  not 


22 


BUILDINGS  OF  REINFORCED  CONCRETE 


be  poured  in  freezing  weather.  Whenever  practicable  forms  should 
be  so  built  that  edges  of  beams,  girders  and  columns  will  be  cham¬ 
fered.  Sharp,  re-entrant  angles  in  concrete  are  sources  of  weakness 
and  defects.  The  sides  of  beams  and  girders  should  be  slightly 
splayed,  say  1  in  8  or  10;  thus  forms  may  be  removed  more  readily. 
In  placing  important  reinforcement  rods  upon  forms  it  is  good  prac¬ 
tice  to  use  special  devices  of  metal,  or  notched  blocks  molded  of 
cement  mortar,  to  insure  the  exact  position  and  spacing  of  bars. is 

Surface  Finish. 

The  strongest  argument  against  all-concrete  buildings  is  the  unsatis¬ 
factory  finish  and  color  of  concrete  masonry.  We  are  only  beginning 
to  understand  how  to  treat  concrete  surfaces.  We  have  a  great  deal 
to  learn  before  concrete  buildings  will  give  a  pleasing  architectural 
effect.  To  me  our  concrete  fronts  are  dull  and  uninteresting.  They 
can  not  be  compared  with  brick,  terra  cotta  and  natural  stone  eleva¬ 
tions.  Where  coloring  has  been  attempted  I  consider  the  results  a 
dismal  failure.  The  best  treatment,  in  my  judgment,  has  been 
achieved  for  buildings  in  which  the  natural  concrete  texture  and  color 
have  been  preserved. 

Waterproofing  of  Concrete. 

Waterproofing  of  concrete  is  another  important  consideration.  There 
are  three  classes  of  treatments;  first,  that  obtained  by  mixing  a  com¬ 
pound  consisting  of  an  impalpable  material  with  the  cement — alum, 
finely  divided  clay  and  soap  solutions  have  been  used  with  consider¬ 
able  success;  second,  that  obtained  by  covering  the  concrete  with  a 
coat  of  asphalt,  and  third,  that  obtained  by  laying  impregnated  paper 
or  felt  against  the  concrete  surface.  To  these  may  be  added  the  par¬ 
tial  waterproofing  which  results  when  curtain  walls,  for  example,  are 
painted  on  the  outside  with  a  rich  liquid  cement  mortar. 

The  subjects  of  concrete  finish  and  concrete  waterproofing  for  the 
past  five  years  have  commanded  much  of  the  attention  of  architects 
and  engineers.  Recently  papers  on  these  topics  have  been  read  at  the 
annual  meetings  or  before  the  conventions  of  a  number  of  national 
societies  to  whom  the  problem  of  reinforced  concrete  building  is 
naturally  of  absorbing  interest.™ 

isForms  for  Concrete  Construction,  by  S.  E.  Thompson;  paper  read  before 
Assn,  of  Cement  Users,  1907 ;  See  also  Scientific  American  Supplement, 
April  27,  1907. 

loFor  further  consideration  I  refer  the  readers  to:  Making  Concrete 
Waterproof,  by  I.  O.  Baker,  Eng.  News,  Vol.  62,  p.  390,  Oct.  7,  1909; 
Discussion  on  Impervious  Concrete;  Trans.  Am.  Soc.  C.  E.,  Vol.  51.  p.  114, 
1903;  The  Permeability  of  Concrete  and  Methods  of  Waterproofing;  by 
R.  H.  Gaines,  Eng.  News,  Vol.  58,  p.  344,  Sept.  26,  1907;  A  Surface  Finish 
for  Concrete,  by  H.  H.  Quimby,  Cement  Age,  Nov.,  1906;  The  Treatment 


BUILDINGS  OF  REINFORCED  CONCRETE 


23 


Expansion  Joints. 

Expansion  joints  are  hardly  required  for  building  work,  but  to  pre¬ 
vent  unsightly  cracks  from  changes  of  temperature  or  from  contrac¬ 
tion  of  concrete  through  setting,  light  metal  reinforcement  should  be 
provided,  running  both  ways,  usually  at  24-inch  centers,  over  the  face 
of  plane  surfaces  of  large  area,  even  when  no  rods  are  needed  to  with¬ 
stand  shearing  or  tensile  stresses  due  to  dead  or  live  loadings.  In 
general,  the  size  and  spacing  of  cracks  may  be  assumed  to  vary 
inversely  with  the  bond  strength  of  the  reinforcing  steel  per  unit  of 
concrete  section.  The  prevention  of  large  cracks  by  means  of  rein¬ 
forcement  is  a  matter  of  using  sufficient  steel  to  force  the  concrete 
to  crack  at  small  intervals.  In  conservative  practice  about  V2  per 
cent  of  steel  is  used  and  gives  satisfactory  results.  In  order  to  dis¬ 
tribute  the  deformation  as  much  as  possible,  a  mechanical  bond  bar 
is  advantageously  selected. 

Concrete  Mixtures. 

In  the  scope  of  this  paper  it  is  not  necessary  for  me  to  consider 
in  detail  the  proportioning,  mixing  and  placing  of  concrete,  or  to  out¬ 
line  completely  specifications  for  suitable  cement,  sand  and  broken 
stone  or  gravel.17  Concrete  preferably  should  be  mixed  by  machine. 
If  mixed  by  hand  it  should  be  spread  upon  a  water-tight  wood  plat¬ 
form.  It  should  be  placed  in  position  immediately  after  mixing  and 
before  initial  set  has  taken  place.  Concrete  for  reinforced  building 
floors,  columns  and  walls  never  should  be  retempered.  Concrete  re¬ 
quiring  retempering  invariably  must  be  condemned.  Mixing  and  plac¬ 
ing  of  concrete,  so  far  as  practicable,  should  be  a  continuous  operation. 
When  work  must  stop  over  night  or  discontinue  for  other  causes, 
special  care  must  be  observed  in  bonding  new  to  older  material.  Con¬ 
crete  should  be  poured  as  a  wet  mixture  and  can  not  be  too  thoroughly 
stirred  and  agitated  in  the  forms  to  insure  a  dense,  uniform  product, 
filling  the  forms  and  surrounding  the  reinforcements  completely;  thus 
avoiding  air  spaces  and  honey-comb  effects.  Fresh  concrete  must  be 
kept  wet  for  at  least  one  week  after  depositing;  it  must  be  protected 


of  Concrete  Surfaces,  by  L.  White,  paper  read  before  Association  of  Cement 
Users,  1907,  see  also  Eng.  News,  Jan.  17,  1907;  The  Artistic  Treatment 
of  Concrete,  by  A.  O.  Elzner,  Eng.  Record,  Jan.  12,  1907;  The  Finish  of 
Concrete  Surfaces,  by  M.  C.  Tuttle,  Boston  Society  of  C.  E.,  also  see 
Eng.  Record,  Dec.  28,  1907;  The  Treatment  of  Concrete  Surfaces,  by  E.  B. 
Green,  National  Assn,  of  Cement  Users;  see  also  Eng.  Record,  Feb.  22, 
1908. 

i7The  Laws  of  Proportioning  Concrete;  by  W.  B.  Fuller  and  S.  E.  Thomp¬ 
son;  Trans.  Am.  Soc.  C.  E.,  Vol.  59,  ,p.  67,  Dec.,  1907. 

On  the  Theory  of  Concrete;  by  G.  W.  Rafter;  Trans.  Am.  Soc.  C  E.,  Vol. 
42,  p.  104,  Dec.,  1899. 


24 


BUILDINGS  OF  REINFORCED  CONCRETE 


from  the  rays  of  the  sun,  and  in  hot  summer  weather  should  be  damp- 
ened  by  sprinkling. 

Only  the  best  brands  of  Portland  cement  should  be  used.  The  con¬ 
tractor  should  be  required  always  to  furnish  cement  subject  to  ap¬ 
proval  or  rejection  by  the  architect  or  engineer,  who  should  submit  the 
cement  to  standard  tests,  such  as  are  prescribed  by  the  Committee  on 
Uniform  Tests  of  the  American  Society  of  Civil  Engineers.  Sand 
should  be  clean,  hard,  sharp,  coarse  and  free  from  clay,  loam,  sticks, 
organic  matter  and  other  impurities.  Screenings  or  crusher  dust  from 
broken  stone,  in  which  term  is  included  all  particles  passing  a  ^-inch 
screen,  may,  by  slightly  altering  the  proportions  of  the  ingredients,  be 
substituted  for  the  whole  or  a  portion  of  the  sand  in  such  proportions 
as  to  give  a  dense  mixture  and  the  same  relative  volumes  of  total 
aggregates.  Gravel,  when  used,  should  be  composed  of  clean  pebbles, 
free  from  foreign  matter,  without  excessively  smooth  surfaces.  The 
broken  stone  should  consist  of  homogeneous  pieces  of  hard  or  durable 
rock,  such  as  trap,  granite  or  conglomerate.  For  floor  slabs  in  build¬ 
ings,  limestone  should  be  avoided  whenever  possible.  In  a  fire  it 
tends  to  pop  or  split  and  may  in  jure  a  floor  slab  when  trap  would  not. 

1  should  object  in  general  to  the  use  of  slag  or  cinder  for  structural 
concrete.  Foundation  concrete  may  contain  stone  of  major  dimensions 
2 y2  inches,  one  cement  to  about  eight  aggregate;  approximately  1 
cement,  3  sand,  5  stone.  Concrete  to  resist  water  pressure,  such 
as  in  basement  floors  and  area  walls,  should  have  stone  not  exceeding 

2  inches,  one.  cement  to  six  of  aggregates;  approximately  1-2-4.  Plain 
wall  concrete  should  have  2  inch  stone,  one  cement  to  seven  and  one- 
half  of  aggregate;  approximately  1-2 y2 -5.  Reinforced  concrete  for 
slabs,  beams,  girders,  curtain  walls,  and  columns  should  have  stone 
never  exceeding  1  in.;  for  thin  slabs  and  walls  with  much  metal 
preferably  not  exceeding  %  in.;  one  of  cement  to  six  of  aggregate, 
approximately  1-2-4.  In  general  the  mixture  of  cement,  sand  and  stone 
should  be  so  proportioned  that  for  the  particular  size  and  fitness  of 
sand  and  stone  the  resulting  concrete  will  be  dense;  that  is,  the  voids 
should  be  filled  as  far  as  practicable.  Any  experienced  concrete 
engineer  can  determine  by  simple  methods  the  exact  scientific  propor¬ 
tions  of  the  three  ingredients.  In  general  for  slender  work  and  com¬ 
plex  reinforcement  rods  the  mixture  should  be  richer  and  the  stone 
smaller  as  the  slenderness  of  mass  and  complexity  of  metal  parts 
increase. 

Economic  Proportions  of  Steel  and  Concrete. 

The  least  costly  beams  and  girders  do  not  result  from  design  calcu¬ 
lations  using  the  highest  permissible  working  stresses  in  steel.  If  the 


BUILDINGS  OF  REINFORCED  CONCRETE 


25 


allowable  compressive  stresses  in  the  concrete  be  fixed  at  400  to  500 
lbs.  per  sq.  in.,  then  the  economic  working  stress  in  the  steel  will 
follow,  given  the  relative  costs  of  steel  and  concrete  per  unit  of 
volume.  For  normal  prices,  a  working  steel  stress  ranging  from 
11,000  to  14,000  lbs.  per  sq.  in.  is  found  economic.  A  prescribed  work¬ 
ing  stress  of  12,000  lbs.  for  average  computations  is  reasonable. 
Unfortunately  architectural  requirements,  such  as  clearances  and  deco¬ 
ration,  so  generally  affect  the  proportions  of  the  beam  or  girder  in 
width  and  depth  that  strict  economy  in  the  proportions  of  concrete 
and  steel  can  not  be  observed. 

Members  with  Reinforcement  Composed  of  Structural  Shapes. 

Columns  with  large  amounts  of  reinforcement  have  been  designed, 
notably  in  the  case  of  the  McGraw  Building,  New  York  City.  In  that 
building  a  structural  column  unit  consisting  of  four  laced  angles  was 
used.  These  units  enclose  a  concrete  mass  binding  it  like  hooping, 
and  are  themselves  encased  in  a  fireproofing  of  concrete.  The  struc¬ 
tural  steel  units  were  designed  to  be  themselves  capable  of  acting  as 
columns  to  carry  dead  load  of  the  structure.  It  is  clear  that,  as  a  gen¬ 
eral  principle,  such  a  scheme  might  be  employed  to  carry  on  the  steel 
frame  at  least  the  false  work  and  dead  load  of  two  or  more  floors, 
thus  enabling  the  placing  of  concrete  to  proceed  simultaneously  on 
several  floors.  In  such  a  design  some  of  the  initial  dead  load  stress 
would  be  applied  to  the  steel  of  the  columns  before  much  of  the  con¬ 
crete  is  placed,  thus  giving  to  the  metal  at  an  early  stage  some  elastic 
strain,  enabling  it  thereby  later  to  carry  greater  stresses  than  deter¬ 
mined  by  the  ratio  of  coefficients  of  elasticity  of  steel  to  concrete. 
This  would  seem  to  be  a  source  of  economy,  but  it  must  be  noted 
that  structural  steel  members  riveted  together  by  lacing  cost  more 
than  plain  rods  with  wire  hooping.  Moreover,  the  initial  dead  load 
erection  stress  must  always  be  uncertain.  It  would  seem,  too,  that 
where  angles  or  other  rolled  shapes  are  used,  offering  broad  plane 
surfaces  of  contact,  the  adhesion  of  the  concrete  to  steel  would  not  be 
so  good  as  for  deformed  bars.  With  such  large  percentages  of  struc¬ 
tural  steel  the  bond  to  the  concrete  is  not  readily  secured.  There  are 
apt  to  be  planes  of  division  or  cleavage  detracting  from  the  mono¬ 
lithic  character  which  should  be  insisted  upon  in  reinforced  concrete 
design. 

Columns  with  rolled  steel  reinforcement  have  been  criticised  severely 
by  some  engineers  and  approved  by  others.  The  subject  is  in  its 
infancy.  The  ideas  involved  might  readily  be  applied  also  to  the  design 
of  main  girders  and  beams.  Indeed,  so-called  unit  frames  of  various 


26 


BUILDINGS  OF  REINFORCED  CONCRETE 


types  have  been  proposed,  particularly  for  reinforced  concrete  beams. 
It  is  entirely  feasible  at  present  to  erect  a  steel  frame  work  capable 
of  carrying  its  own  load,  false  work  and  erecting  machinery,  later  to 
be  clothed  in  concrete.  I  remember  that  one  building  was  so  con¬ 
structed  in  San  Francisco,  namely,  the  Owl  drug  store’s  building  on 
Mission  Street.  There  appear  to  be  some  advantages  in  such  a  sys¬ 
tem.  It  insures  the  definite  placing  of  the  reinforcement  metal  and 
enables  a  designer  to  know  that  the  exact  connections  will  be  made 
which  he  provided,  thus  securing  strength  at  the  joints  of  the  struc¬ 
ture.  Moreover,  more  definite  continuity  in  columns  and  between  col¬ 
umns  and  girders  would  result  without  relying  too  much  upon  the  intel¬ 
ligence  and  integrity  of  t  he  field  foreman.  I  question,  however, 
whether  a  system  of  this  character  will  ever  become  fashionable.  With 
its  structural  merits  it  has  the  attendant  defect  of  increasing  costs. 
At  any  rate,  in  the  present  state  of  reinforced  concrete  construction 
it  may  be  applied  successfully  to  single  units  such  as  columns  and 
beams,  but  not  to  the  whole  structure  as  one  articulated  metal  cage. 

Fire  Resisting  Qualities  of  Reinforced  Concrete. 

There  are  certain  qualities  of  reinforced  concrete  construction  which 
must  appeal  to  fire  insurance  men.  All  evidence  to  date  justifies  us 
in  concluding  that  the  steel,  where  properly  imbedded  in  the  concrete, 
will  be  protected  from  corrosion.  It  is  admitted  that  concrete,  with 
the  possible  exception  of  brick,  gives  a  most  satisfactory  fire  protec¬ 
tion.  Laboratory  fire  tests  and  experiences  from  the  conflagrations  of 
Baltimore  and  San  Francisco  indicate  that  from  2  in.  to  3  in.  of  con¬ 
crete  will  offer  practically  a  complete  protection  to  steel.  From  per¬ 
sonal  observation  in  San  Francisco  it  is  my  opinion  that  properly 
designed  reinforced  concrete  members  like  columns  and  beams  will 
safely  resist  any  ordinary  fire;  provided  the  members  have  their  metal 
sufficiently  coated  with  concrete.  In  order  to  cut  down  the  expense  of 
reinforced  concrete  buildings  in  comparison  to  buildings  with  struc¬ 
tural  steel  frames  it  has  been  too  much  the  custom  to  decrease  costs 
by  eliminating  concrete,  which  would  be  specified  eagerly  as  a  protect¬ 
ing  surface  to  the  structural  steel  members  of  an  alternative  building. 
It  is  further  my  observation  in  examining  reinforced  concrete  buildings 
constructed  in  San  Francisco  during  the  last  three  years  that  their 
secondary  parts  are  composed  too  commonly  of  combustible  materials. 
It  is  a  great  mistake  to  spend  much  money  on  a  reinforced  concrete 
frame  and  then  finish  the  floors,  partitions  and  casings  chiefly  of  wood. 
Partitions,  particularly,  have  been  the  great  offenders  in  this  respect. 
What  would  otherwise  be  an  ordinary  fire  would  become  severely 


BUILDINGS  OF  REINFORCED  CONCRETE 


27 


destructive  where  a  large  part  of  the  trim  of  the  building  in  close 
contact  with  the  structural  concrete  is  highly  combustible.  It  should 
be  remembered  that  a  well-built  reinforced  concrete  frame  will  cost 
money  to  take  down  when  once  too  severely  injured  by  a  fire.  This 
element  of  cost  in  razing  a  fire  loss  ought  to  be  considered.  In  the 
case  of  factories  and  warehouses  the  more  inflammable  the  contents 
to  be  stored,  the  less  should  be  the  inflammable  fixtures  of  the  build¬ 
ing,  the  thicker  also  the  concrete  fire  protection.  My  argument  in  this 
respect  is  much  akin  to  remarks  which  might  have  been  made  con¬ 
cerning  first-class  class  B  buildings  which  were  destroyed  in  1906  in 
San  Francisco.  I  refer  to  structures  with  self-supporting  outer  walls 
and  independent  interior  frames  partially  of  rolled  steel  and  cast  iron 
with  much  wood  for  secondary  parts.  One  of  the  most  costly  examples 
was  the  Emporium  Building;  a  less  notable  instance  the  Cowell  Build¬ 
ing.  To  be  sure,  both  structures  were  subjected  to  most  intense  heat, 
due  to  the  nature  of  their  stored  contents,  aside  from  the  inflammable 
fixtures  of  the  structures  themselves.  The  ruins  of  such  buildings 
after  great  fires  always  offer  great  hindrance  to  rapid  reconstruction. 
A  great  conflagration  destroys  them  completely  so  far  as  repairs  are 
concerned,  but  leaves  the  remains  of  twisted  steel  members  and 
cracked  masonry  in  a  sufficient  stiff  and  tangled  mass  to  make  it 
necessary  to  expend  large  sums  of  money  and  to  consume  much  time 
in  disposing  of  the  wreck. 

Municipal  Building  Ordinances  Versus  Building  Inspection. 

While  my  chief  object  has  been  to  discuss  reinforced  concrete,  you 
will  pardon  me  if  I  refer  to  some  matters  affecting  not  merely  rein¬ 
forced  concrete  building  construction,  but  the  construction  of  buildings 
in  general  in  a  city  like  San  Francisco. 

Immediately  after  the  fire  the  building  ordinance  was  revised;  as 
well  it  might  be.  The  old  ordinance,  though  it  was  spoken  of  as  a 
building  law,  was  really  composed  of  many  different  and  sometimes 
conflicting  enactments  of  the  Board  of  Supervisors  made  at  different 
times  during  the  last  ten  years.  Of  course  it  was  full  of  contradictory 
clauses  and  open  to  the  criticism  that  it  was  indefinite  and  of  poor 
arrangement.  While  the  present  building  law  may  be  criticised  also, 
it  is  a  vast  improvement  upon  the  old  ordinance.  An  ordinance  natu¬ 
rally  can  not  be  perfect.  No  such  instrument  ever  was  or  could  be. 
Ours  has  many  defects  and  contains  a  number  of  articles  that  should 
be  changed  as  soon  as  possible.  Any  one  remembering  the  circum¬ 
stances  and  pressure,  however,  under  which  the  new  ordinance  was 
arranged  will  have  considerable  respect  for  the  authors  of  the  law, 


28 


BUILDINGS  OF  REINFORCED  CONCRETE 


for  it  is  based  on  sound  practice  and  good  scientific  judgment.  It  is 
gratifying  to  note  that  for  some  time  past  a  revision  of  the  building 
law  has  been  under  contemplation.  While  we  will  be  anxious  to  use 
the  revised  ordinance,  it  is  to  be  deplored  that  it  may  have  little 
practical  effect;  for  one  of  the  most  unfortunate  conditions  affecting 
building  in  San  Francisco  is  the  lack  of  sufficient  inspection  on  the 
part  of  the  building  department.  Earlier  in  my  remarks  I  have  given 
examples  of  actual  buildings  built  since  1907  in  which  the  law  has  been 
grossly  disobeyed;  that  is,  its  structural  prescriptions.  The  law  may 
be  conservative  and,  if  rigorously  enforced,  would  considerably  in¬ 
crease  the  structural  cost  of  a  building.  But  such  an  argument  can  not 
justify  the  acceptance  of  designs  going  to  the  other  extreme  of  reck¬ 
less  economy,  leading  to  the  erection  of  buildings  of  questionable 
stiffness,  if  not  of  certain  weakness.  It  is  the  details  of  San  Fran¬ 
cisco  buildings  which  are  inspected  and  not  their  larger  requirements 
for  strength.  It  is  more  likely  that  an  owner  is  obliged  to  place  a  petty 
fire  escape  in  accordance  with  the  letter  of  the  ordinance  than  that 
he  is  restrained  from  erecting  a  frame  so  slender  that  reinforced 
beams  are  stressed  to  1200  lbs.  per  sq.  in.  in  the  concrete. 

It  would  not  be  just  to  make  these  strictures  upon  the  building  de¬ 
partment  and  its  inspecting  force  without  at  the  same  time  observing 
that  they  are  hardly  to  blame.  At  present  the  city  does  not  provide 
an  adequate  force.  We  can  not  expect  the  limited  force  to  give  due 
attention  to  all  matters  which  our  building  ordinance  proposes  shall 
be  considered  in  connection  with  the  erection  of  buildings.  The  staff 
as  now  constituted  is  more  capable  to  examine  plumbing  and  electric 
fixtures  than  to  check  the  stress  sheets  for  the  frame-work  or  foun¬ 
dations.  What  we  need  is  emphasis  on  inspection  and  not  on  a  build¬ 
ing  ordinance.  A  building  ordinance  should  not  be  looked  upon  as  a 
text  book  or  as  a  hand  book  whose  purpose  is  to  instruct  a  greenhorn 
in  engineering  or  architecture.  A  building  law  can  not  and  never  should 
be  a  specification.  It  ought  to  be  as  terse  and  to  the  point  as  possible 
without  treating  details,  and  have  for  its  object  the  protection  of  the 
city  and  the  general  public  against  persons  who  want  to  build  too 
poorly.  The  building  ordinance  should  provide  definite  penalties  if 
its  clauses  are  broken.  While  an  ordinance  in  part  partakes  of  the 
nature  of  a  specification,  it  should  only  do  so  as  far  as  it  is  necessary 
to  elucidate  some  of  its  provisions.  As  a  law  the  ordinance  tells  what 
shall  be  done,  and  in  order  that  its  provisions  may  be  enforced,  it  in 
some  cases  tells  how  the  work  shall  be  done.  It  is  a  function  of  a 
specification  to  tell  how  to  do  a  thing.  The  sole  and  vital  reason  for 
the  existence  of  a  building  ordinance,  however,  is  merely  to  tell  what 


BUILDINGS  OF  REINFORCED  CONCRETE 


29 


to  do.  What  is  needed  in  San  Francisco  is  not  so  much  a  newly  revised 
ordinance  with  greater  detail  of  specifications,  but  rather  the  present 
ordinance  with  a  few  modifications  and,  if  possible,  greater  brevity, 
coupled  with  an  efficient  building  department  commanding  the  services 
of  properly  trained  inspectors.  I  should  be  glad  to  see  more  recogni¬ 
tion  in  our  building  law  of  those  clauses  relating  to  fire  hazard,  fire 
protection  and  prevention  which  are  outlined  in  the  building  code 
recommended  by  the  National  Board  of  Fire  Underwriters. 

Fire  Testing  Stations. 

Immediately  after  our  fire  it  was  the  desire  of  some  members  of  the 
building  community  to  establish  a  fire  testing  station  in  San  Francisco. 
The  scheme  had  the  earnest  support  of  many  architects,  engineers, 
contractors,  and  manufacturers  of  building  materials.  Representa¬ 
tives  of  the  city  fire  department  and  municipal  government  were  inter¬ 
ested.  The  laboratories  of  the  universities  were  ready  to  co-operate. 
It  was  found  that  a  fire  testing  station  means  an  expensive  establish¬ 
ment  and  that  it  costs  money  to  run  one  on  an  efficient  and  practical 
scale.  It  was  argued  by  some  who  visited  us  at  that  time  from  the 
East  that  we  had  no  need  for  a  fire  testing  station;  that  it  was  useless 
to  duplicate  results.  We  were  told  that  we  might  as  well  save  our 
money  and  benefit  by  Eastern  experiments.  It  is  true  that  we  have 
learned  much  from  the  fire  testing  station  conducted  at  Columbia 
University  in  co-operation  with  the  building  department  of  the  city  of 
New  York.  We  can  benefit  by  perusing  the  reports  of  W.  C.  Robin¬ 
son,  Chief  Engineer  of  the  Underwriters’  Laboratories  at  Chicago. 
Reports  from  the  Insurance  Engineering  Experiment  Station  at  Boston 
and  from  the  special  Testing  of  Materials  Laboratories  of  the  U.  S. 
Geological  Survey,  at  St.  Louis,  are  always  instructive.  It  may  be  that 
it  would  be  a  mistake  for  us  to  establish  a  fire  testing  station  on  the 
Pacific  Coast.  But  I  am  not  convinced  that  this  is  the  case.  California 
is  separated  by  mountains  and  deserts  from  the  Mississippi  Valley 
almost  as  though  an  ocean  intervened.  We  have  our  distinct  local 
problems.  Beside,  and  what  is  more  to  the  point,  it  is  worth  some¬ 
thing  to  us  to  make  a  few  tests  of  our  own.  There  is  a  distinct  ele¬ 
ment  of  value  in  having  been  present  at  and  concerned  with,  or  having 
been  an  eye-witness  to  special  fire  tests  of  materials  used  in  or 
furnished  by  the  local  market. 

Conclusions. 

In  my  opening  remarks  I  referred  to  a  possible  salutary  relation 
existing  between  fire  insurance  underwriting  and  principles  of  engi¬ 
neering  design  as  factors  of  knowledge  worth  while  to  an  insurance 


30 


BUILDINGS  OF  REINFORCED  CONCRETE 


man.  I  have  concluded  with  reference  to  the  status  of  the  San  Fran¬ 
cisco  building  ordinance  and  the  worth  of  a  fire  testing  station.  Be¬ 
tween  these  digressions  I  have  attempted  to  give  you  what  I  thought 
might  be  a  suggestive  description  of  the  present  art  of  building  in 
reinforced  concrete.  I  have  attempted  to  indicate  that  almost  no  type 
of  future  construction  will  be  entirely  free  of  parts  in  reinforced  con¬ 
crete.  I  have  reminded  you  that  for  the  highest  types  of  building 
reinforced  concrete  is  used  for  most  essential  parts  and  may  be  used 
to  the  entire  exclusion  of  other  forms  of  construction.  I  have  outlined 
the  important  specifications  for  safe  stresses,  for  economic  proportions 
of  parts  of  the  frame,  and  for  the  distribution  of  concrete  and  metal. 
One  of  my  main  objects  was  to  explain  that  whenever  used,  reinforced 
concrete  design  requires  a  high  degree  of  engineering  talent.  While 
I  do  not  advocate  its  use  for  high  buildings,  I  trust  I  have  made  clear 
that  it  can  be  recommended  unconditionally  for  heavy  construction, 
such  as  warehouses,  or  for  low  buildings,  such  as  schools  and  hos¬ 
pitals.  It  has  effective  fire  resisting  qualities.  We  have  heard  so 
much  about  earthquakes  that  I  hesitate  to  use  the  term,  but  I  must 
observe  that  reinforced  concrete  lends  itself  most  readily  to  sensible 
earthquake  construction. 

In  short,  for  buildings,  reinforced  concrete  is  a  most  valuable 
material.  We  have  much  yet  to  learn,  but  always  we  will  have  to  be 
masters  of  engineering  arts  to  use  the  combination  of  steel  and  con¬ 
crete  intelligently.  It  is  no  wonder,  therefore,  that  some  structures 
have  been  failures.  It  is  rather  to  be  wondered  that  so  few  structures 
have  collapsed.  When  a  new  type  of  building  has  been  suddenly 
introduced,  we  should  rather  be  surprised  if  we  could  not  recall  cases 
where  owners  have  learned  from  bitter  experience  that  they  might 
have  built  more  cheaply  with  structural  steel.  Nevertheless,  sum¬ 
ming  up  all  arguments,  for  and  against,  I  believe  I  could  not  be 
considered  partisan  to  reinforced  concrete  in  recommending  it  gener¬ 
ously  to  the  attention  of  the  building  community  and  particularly  to 
gentlemen  interested  in  fire  insurance. 


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BUILDINGS  OP  REINFORCED  CONCRETE 


31 


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32  BUILDINGS  OF  REINFORCED  CONCRETE 

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